Process and apparatus for the production of phosphoric acid



June 17, 1924. 1,497,727

B.G.KLUGH PROCESS AND APPARATUS FOR THE PRODUCTION OF PHOSPHOHIC ACID.Filed Dec. 7, 1920 '4 Sheets-Sheet 1 I BYzZZ ATTORNEY June 17 1924.

V B. G. KLUGH PROCES AND APPARATUS FOR THE PRODUCTION OF PHOSPHORIC ACIDFiled Dec. '7 1920 2 5heet=-5heet 3 INVENTOR ATTORNEYraame'dlquneiia1924;

' TUNITED STAT P TENT OFFICE.

Barnum: c. KLUGH, or ANNISTON, ALABA A, ASSIGNOR '1'0 FEDER Lrrrosrnonus comm, our BIRMINGHAM, ALABAMA, A CORPORATION or ALABAMA.

'- mocrss AND ArrAnAros FOR THE rn'onuc'rron or rrrosrnoar'c ACID.

Application filed December 7, 1920. Serial No. 429,016.

To all whom it, coace'm:

.Be it known that I, BETHUNE G. KLUGH, a citizen of the United States ofAmerica,

residing at Anniston, in the county of Cal- I .the production of Iprecipitationor other suitable'means.

It has for its object the smeltin' of each unit of phosphorus involvedwith ess electrical energy, hence lower cost, than is'possible in thepresent state of the art, and the provision of means for efi'ecting'suchsaving in a practical manner while at the same time facilitating theessential steps in the process.

I will illustrate by thermal calculations the heat units involved in theelectrical smeltingv of an assumed quantity of mate rials in theprocess. The chemical reaction which fulfills the conditions involved insuch smelting operation is as follows:

The relative weights of hypothetically pure materials involved in thisequation per pound of phosphorus is as follows:

. Lbs. Pho horus 1 (0a P- o 5 0arbon -A .967 3(0aO)2(SiO 4..645 CO 2.250

4929 'cal0ries,'or 1.24 times as much heat as is required to befurnished by electrical energy. It is obvious that any of the calories(usually wasted) from the combustion of the phosphorus and carbonmonoxide, that can be absorbed by the stock in the smelting zone willreplace an equivalent amount of electrical energy, and there-. by resultin equivalent saving in smelting costs. The theoretical temperature ofcom bustion with cold air without excess of the relative quantities ofphosphorus and carbon monoxide from the hereinbefore described charge,is about 24=OO 0., that with the air without excess for combustionheated to 600 0., is'about 2700 0., and that with air without excess forcombustion heated to 1000 0., about 2900 0. It is obvious that the rateof heat absorption by the stock will be increased many times by thehigher temperature of combustion of the gases in contact therewith.

The herein described invention discloses a. practical means of causingthe stock-to abfrom the heat of combustion of the gases sorb a maximumquantit of said heat from the combustion of the p osphorus and carbonmonoxide, and furthermore gives advantages in the conducting of all thefeatures of'the; operation. Attempts have been made to absorb a pdrtionof this combustion heat in the stock by passing the burn- King andheated gases over and through the stock in transit to the electricfurnace through revolvin tubes and inclined or vertical shafts. llinvolve a clumsy and impractical mechanical equipment, interfere withthe proper distributionof the stock in the furnace, and entrainquantities of dust in the gases, as well as present manyother"undesirable features of operation.

I will now describe my invention so that those skilled in the art mayclearly understand and practice it.

Referring to the drawings, like symbols in the different figuresindicate like parts; Fig. l is a horizontal sectional view taken on theline 11 of Fig. 2.

Fig. 2 is a longitudinal sectional view on the line 2- 2 of Fig. 1.

Fig. 3 is a transverse vertical section ah view through the furnace.

Fig. 4 is an enlarged cross sectional view taken on the line 44 of Fig2.

Fig. 5 is an enlarged cross sectional view furnace through the annularspaces E,

into respective gas mains which exist between the electrodes F and theirrespective inwardly projecting stock feed refractory rings G. The stockwithin this space seals the gases within'the combustion chamber againsttheir outward passage. The furnace is further provided with gas, assagesH' Hat either end with which com ustion chamber A communicates. Thesepassages are constructed with an elevation of the arch roof C, andof'bridgewall I, I, so that the incoming combustion air from one end, ashereinafter described,

willbe projected downwardly upon the stock adjacent thereto, and effectdirect com-' bastion of the gases emanating from the surface of saidstock. The gas passages H and continue J, "which are constructedrespectively in duplicate as shown, and connect directly intoregenerative checker work L and L, through which the gas passesrespectively to the batteries of multiple coolers K and K and thenthrough their respective manifolds M and M, and through pipes N, N, intothe respective electrical precipitators'O, 0', shown and H comunicatedirectl in vertical section in Fig. 4. .The two re spectiveprecipitators in Fig. 4 show the lower gas chambers P, P with pipes Q, Q

communicating to the upper'gas chamber R, R and thence through pipes S,S. The reversing valves T, T jointly control the flow of the gases (orair). so that as the valves are set in the figures, .the gases fromprecipitator 0, from which the phosphoric acid has been removed therein,pass out through waste stack U. The air blower V delivers air underpressure through manifold W, W, and with the valves T, T set as shown,is closed against gas pipe S and open to pipe S. The reversal of the gasand air movement is then entirely controlled bymeans of the valves T, T,whose re- 'spect-iv stems X, X are actuated reciprocally t rough thecommon connecting cable Y. 1

Having explained the apparatus throughthe figures I will briefly discussthe operation of the process therewith with attention to advantagesgained thereby. 1

the smelting zone within the-stock and pass out uniformly. over theentire to surface of the stock within the furnace. tithe same time freshcold stock is being constantly suppliedthrough the' stock feed openingssurroundin the electrodes, and responsive to the continuous demands ofthe fusion zone, is automatically delivered and distributed over thesaid top surface of the stock within the furnace.

If the'phosphorus and carbon monoxide be burned witha large excess ofair or if the combustion of said gases is completed other thanindirect'contact with the top surface of the freshly supplied stock, or ifthe gases pass out from said surface of the stock too quickl therewillbe very little of the heat evo ved from said combustion combustion tothe highest attainable degree,

I cause the greatest flow of heat units evolved in said combustion ofgas to the incoming stock, and hence provide the greatest possibleamount of heat in said stock to replace that required to be supplied byelectricalenergy.

In the construction of the furnace herein described, I provide theeatest possible area of the top surface of t e stock within the furnace,and said area is further so placed in the furnace as to cause the gascombustion to proceed over the said entire surface. The said stock beingdelivereduniformly and in a thin layer over said surface presentscontact to the largest-possible volumeof burning gases therewith whichis most conducive to absorption of the-heat therefrom. I

In the operation of the hereindescribed invention, the products ofcombustion, after passing out one end of the furnace, have theirsensible heat absorbed progressively by the refractory materials in theregenerative chamber through which they pass. The flow of the gases ismaintained in this direction until the temperature rise in the fartherend of said regenerative chamber shows that the maximum absorption ofheat has beenreached, whereupon the direction of. the gases from thecombustion chamber A is reversed and the 'air for combustion forcedthrough the regenerative chambers to be heated therein and passed at ahigh temperature into the combustion chamber, thuscoming in directcontact withthe evolved. phosphorus and carbon monoxide, and effectingtheir combustion with the highest practicably attainable temperature ofcombustion.- I do not confine myself to the horizontal type ofregenerative furnace, or to the proportionate dimension shown in thedrawing, but wish my herein described invention to include anyarrangement of regenerative chamber, in which the materials ofconstruction present the best design as to size, area, weight, or volumefor absorbing the heat from gases passing thereover, or

thereabout, and for storing up said heat for disbursement to lowertemperature gases subsequently passed thereover or thereabout.

As shown in the drawings, the air for combustion as it is reversedpasses alternately through the entire passage last traversed bythe gasand thus its heat absorbing capacity will take up the heat which hasbeen stored up in the passage by the gases. Furthermore, by forcing theair for combustion through the electrical precipitator in which thestream of gaswas last treated,

and through the entire length of the gas passage before reversion, allof the P 0 left in the precipitator and passage is conducted back Withthe stream of combustion air and forced through the furnace combustionconditions requires cleaning of insulators,

' wires and pipes periodically in order to maintain its efliciency inits precipitatin functions. Thus during theperiod in whic the combustionair is being driven through the precipitator as a part of its cycle ofoperation, the air within presents ideal conditions for workmen toperform all cleaning or repairing desired without interruption of thecontinuous operation of the acid produc-' .tion and collection. Ipropose to provide air locks Z, Z for entry and exits in the upper andlower chambers of the precipitators without interference with thecurrent of .combustion air being passed therethrough.

p der suction, or under pressures The exact volume of air 1' uired forcombustion of the'gases 1n the mace 1s governed by the speed of theblower EV. My

system as shown in the herein describedinvention corrects certain verytroublesome "conditions prevailing in the usually practiced methods ofhandling the ases unlow atmospheric-pressure. The objections to suchprocedure, which are corrected by producing my invention ashereindescribed, are

(1) Under reduced pressure air leakage, which increases greatly thevolume of gas to be handled, occurs through vents that are scarcelydetectable, while under pressure, such leaks become obvious, and onlyresult in a loss of gas or air without proportionately overloading thecapacity of the handling and collecting apparatus.

(2) The passing of the P 0 bearing gases through a fan or suction pumpis very objectionable on account of the condensing and corrosivecharacteristics thereof, which shorten the life and efficiency of thefan, whereas inplacing the entire cycle under pressure by means offorcing the combustion air through the entire cycle, I cause only air tobe handled through the pump, thus obviating all the diificultiesmentioned.

(3) Intthe hereinbefore mentioned proportions of phosphorus, and carbonmonoxide combustion, the weight of products of combustion is 13.9 whilethe weight of air required for said combustion is 10.7. Moreover, theair is cool and relatively dense.

whereas the gases are hot and greatly expanded. By handling only the airI- have a medium of less heat and greater density. Thus the smallerquantity to be handled as Well as its better handling qualities is decidedly in favor of the hereindescribed procedure.

(4) I avoid passing the P 0 gases through any valves, as none areinterposed in the system except between an air intake and theprecipitators. On account of the tendency of the P 0 to condense on andcorrode or render sticky all parts of operating mechanism with which itcomes in contact, this advantage, from an operating view point, hasgreat value.

In case I collect the P 0 or derivatives thereof by means other than bythe electrical precipitator or .in case it is not practicable to use theduplicate precipitators, and

it is desirable to unite the alternative mains into one prior toconducting the cooled P 0 bearing gases into the final collectingapparatus, I chang'e'the location of the air blower and reversing valvesas shown in Figs. 5 and 6. The apparatus then remains the same as shownin Figs. 1 to 4 up to the manifold pipes M, M. These pipes are connectedrespectively. to the interposed valve chambers W, W, containingrespectively the reversing valves T, T and connected overhead by themanifold N" to a pipe N leading to any collector. The blower V deliversair at the required pressure to the valve chamber W and W and accordingto which of the Valves T, T is open, the air flows through one course tothe combustion chamber while the gases return through the other courseto manifold M or M and flow past the valve T or T, Whichever is closedto the air, and thence pass through manifold N" and pipe N' to thecollector. In all other respects except the use of one collector and theloss of the feature of 'fiowing the air through the collector not inuse,this alternative process is similar in its functions to that alreadydescribed.

The method of utilizing the heat of the gases to highly preheat thestock in the furnace is the essential basis of my invention. Bypreheating the air supply I can greatly raise the temperature ofcombustion of the gases and thereby, notwithstanding their short stay inthe presence of the stock, I can succeed in transferring a maximumquantity of heat units into the stock. To avoid excessive waste of heatin the high temperature attained by the gases in my process it isdesirable to recover as much of this heat as possible and this is doneby recuperating it by a regenerative apparatus in which the combustionair supply is heated. These higher combustion temperatures in thefurnace necessitate great care for the protection of the electrodesagainst oxidation by the combustion air and this I accomplish bysurrounding each with an entering column of cold stocl' which flowscontinuously responsive to the demands of the fusion zone.

The carbon which is added to the smelting stock for reduction in thesmelting is most effective therefor, when in a finely divided state, saynot over one-eighth of an inch in size. The phosphate rock and siliciousfiuxing materials being of larger size and the proportioned mixturebeing fed through the stock feed opening as shown, into the furnace, andthe stock assuming in its natural angle of repose within said furnace,viz, a sloping section, will cause the coarser ma terials to roll towardthe outer sides of the furnace or away from the electrodes, While thefinely divided carbon tends to cling near the electrodes, especially ina sectional column formed about the lower edge of the internallyprojecting stock feed ring. In this way the carbon for reduction in thestock is protected from oxidation by the highly heated combustion airwithin the combustion chamber by the non-combustible coarser portion ofthe stock covering it during its passage to the smelting zone. t

I have found this tendency of segregation of the reducing carbon in thedescending column of stock within the furnace is ad vantageous in theconstruction of furnace shown. because its descent in a column about theelectrode, protects said electrode from direct oxidation from thereducible oxides in the stock, by preventing direct contact of the saidfurnace justabove the slagging 66 zone, which is the natural zone inwhich said reducing carbon performs its function.

Having thus described my invention, what I claim as new 'and desire tosecure by Let 'ers Patent,- is 70 lJA process for the smelting ofphosphatic material in an enclosed electric furnace, which consists inadmitting air for the oxidation of gases as evolved in said smeltingoperation, and preheating said airto raise the temperature of combustionof said gases in the furnace.

2. A process for the smelting of phosphatic material in an enclosedelectric furnace, which consists in regulating the volume of airadmitted to that requisite for the oxidation of the gases as evolved insaid smelting operation, and preheating said air to raise thetemperature of combustion of a said gases in the furnace.

3. A process.for the smelting-of phosphatic material in an enclosedelectric furnace, which consists in admitting 'air for" the oxidation ofgases as evolved in said smelting operation, and utilizing the heat in ithe outflowing gases to preheat the air admitted to the furnace andraise the point ofcombustion of the gasestherein.

4. A process for the smelting of phosphatic material in an enclosedelectric furnace, whichconsists in regulating the volume of air admittedto that requisite for the oxidation of the gases as evolved in saidsmelting operation, and utilizing the heat in the outfiowing gases topreheat the air admitted to the furnace and raise the point of combus-'tion of the gases therein.

5. A process for the smelting of phosphatic and carbonaceous material inan enclosed electric furnace, which consists in regulating the volume ofair admitted to that requisite for the oxidation in the furnace of thephosphorus fumes and carbon monoxide gases as evolved, and transferringheat from the waste gases to the air supply I to thereby reduce thegases to the requisite temperature for the recovery of phosphoric acidand to raise the air to a high temperature to thereby increase thetemperature of combustion of the gases in the furnace.

6. A process for the smelting of phosphat- -ic material in an enclosedelectric furnace,

which consists in forcing into'the furnace an air current under apredetermined pressure which will admit the requisite volume of air tooxidize the gases as evolved in the furnace, and utilizing said aircurrent to expel the gases from the furnace into a collector. h

7. A process for the smelting of phosphat- '125 ie material in anenclosed electric furnace, which consists in forcing into the furnace anair current under a predetermined pressure which will admit therequisite volume of air to oxidize the gases as evolved in the furnace,utilizing said air current to expel the gases from the furnace into acollector.

not at the time containing the evolved gases' 9. A process for theproduction of phosphoric acid by an electric furnace, which consists inproviding regenerative gas pas sages and respective electricprecipitators therefor, forcing an air blast alternatively through apassage and its precipitator to preheat the air, oxidize theev'olved-gases in the furnace and expel them through the other passageand precipitator.

10. A process for the smelting of phosphatic material in an electricfurnace, which consists in preheating the air supply for the furnace,admitting the preheated air alternatively at opposite ends of thefurnace in volume sufficient for the oxidation of the gases as evolvedin the furnace, and causing the gases while burning with an increasedtemperature of combustion to flow slowly through the furnace and aboutthe entering stock to preheat the latter.

11. A process for the smelting of phosphatic material in an enclosedelectric furnace, which consists in feeding fresh stock continuouslyresponsive to the demands of the fusion zone. providing ample spaceabove the stock for the combustion of the evolved gases about theentering columns of stock, admitting air in the approximate volumerequisite for the oxidation of only the gases as evolved, preheatingsaid air to greatly increase the temperature of combustion of the gasesin the furnace, causing the burning gases to pass slowly over and aboutthe entering columns of stock as the gases pass out of the furnace, andtransferring heat from the abnormally heated gases leaving the furnaceto preheat the entering air supply.

12. A process for the smelting of phosphatic material in an enclosedelectric furnace, which consists in providing a continuous feed of stockresponsive to the de mands of the fusion zone, providing a combustionspace for the burning of the gases above the stock, utilizing the stocktos urround and protect the electrodes, preheat-- ing the air enteringthe furnace to raise the temperature of combustion of the evolvedgases,regulating the volume of air admitted approximately to that-required forthe oxidation of said gases as evolved, and causing the burning gases topass slowly over and around the entering stock columns to radiate a highpercentage of their heat to the stock before it enters the fusion zone.

13. An apparatus for the smelting of phosphatic material in an enclosedelectric furnace which comprises regenerative chambers connected withthe furnace, phosphoric acid recovery apparatus to which the gases areconducted through said chambers alternatively, and means to admit theair supply for the furnace to the regenerative chamber not at the timeconducting gases, to preheat said air supply.

14. An apparatus for the smelting of phosphatic material, whichcomprises an enclosed electric furnace, a pair ofregenerative chambersconnected thereto, an acid collector for each chamber, means to causethe air supply for the furnace to fiow through the collector and chambernot receiving the gases, and valve means to reverse the flow of thegases.

15. An apparatus for the smelting of phosphatic material, whichcomprises an enclosed electric furnace, a pair of regenerative chambersconnected therewith, a collector means for the gases fiowin through saidchambers, air ducts connecte to the gas discharge ends ofsaid chambers,reversing valves to alternatively admit air to one chamber and excludeit from the other, and a blower to induce a forced current of air toflow through a chamber and enter the furnace in a preheated condition,

16. An apparatus for the smelting of phosphatic material, comprising anenclosed electric furnace, a pair of re enerative chambers connectedthereto, a co ector for each chamber, an air manifold connected to saidcollectors, a blower to force a current of air into the manifold, andreversing valve means to direct the air through said collectors andchambers alternatlvely to reverse the direction of flow of the gases vindependently of valves exposed to such gases and to preheat the air suply to the furnace.

17. The process for e ectrically smelting phosphatic material with areducing agent, which consists in mingling the reducing agent ina-finely divided state with coarser particles of phosphatic material andfeeding said mixture by gravity flow into an electric furnace responsiveto the demands of the fusion zone through an overhead opening,'

causing the coarser particles to overlie the finer particles whichcollect in anddescend to the fusion zone through the center of the stockcolumn;

18. The process for electrically smelting phosphatic material with areducing agent, which consists in mingling the reducing agent in afinely divided state with coarser center of the stock column, andadmitting particlesof phosphatic material and feedpreheated air to thecombustion chamber 10 ing said mixture by, gravity flow into ansurrounding the stock column in the furnace. electric=furnace responsiveto the demands In testimony whereof I aflix my signature.

of the fusion zone through an over ead opening, causing the coarserparticles to BETHUNE overlie the finer particles which collect inWitness: 1

and descend to the ,fusion zone through the Nomm WELsH.

